Up until now, this type of drawing-off device simply allows, by contact with the liquid to be drawn off, either the supply of a liquid of interest which it contains or the withdrawal of another liquid of interest present in a container.
Such devices in general consist of hollow pipettes or needles linked to pumps. Some that are more sophisticated allow cleaning of the external walls of said pipettes or needles, which have been soaked in the liquid drawn off or to which additional liquid has been added. That is the case for example in the patent application WO-A-99/27973 filed under the priority of 27 Nov. 1997 by the applicant. It relates to a method for decontaminating a hollow metal needle intended for drawing off and/or distributing a contaminating liquid, the needle cooperating with electric power supply means, which make it possible to establish an electric current in the needle in order to decontaminate and preserve the integrity of said needle for the purpose of its reuse. Others are equipped with means, which avoid making these external walls of the drawing-off components dirty, as is the case in patent application WO-A-99/50674 filed under priority of 1st April and of 22 Jun. 1998 by the applicant. This application relates to a method for drawing off a biological sample by means of a suction/delivery apparatus such as a manual or automatic pipette incorporated or not incorporated into an automated machine. However, it also relates to a method for detecting the free surface of a biological sample, an apparatus for drawing off a sample, such as a pipette, and an apparatus for detecting the free surface of a biological sample.
However, when a liquid is added or even optionally withdrawn from a container, such as a tube, a cavity of a microtiter plate, splashes may be produced and drops may thus form on the inside walls of this container. The problem then lies in the fact that these drops contain essential components, which may be useful to a subsequent biological reaction, and in the fact that as these components are not present in the liquid present at the bottom of said container, they cannot participate in said reaction. Thus, in the case of nucleic acids, the quantities of these nucleic acids extracted from cells by lysis or any other technique are few. It is therefore desirable to amplify these molecular targets by adding amplification primers and detection probes. If isolated drops contain even only part of these biological components: targets, primers and/or probes, the amplification and/or the detection reaction that will follow will be disrupted. The disruption will be all the more great if it is desired to perform a quantitative detection and not merely a qualitative detection of the target.
Another problem is the determination of a volume of liquid present in a container. Some controls are sometimes necessary in order to know precisely the volume of liquid distributed into a container or a series of containers. In this case, it is necessary to know precisely said volume. As a result, the presence of a drop or drops that has (have) not been recovered or that cannot be recovered can generate erroneous vales and affect the final result.
No document of the state of the art provides solutions to these problems.